In the past studies, various natural fibers such as flax, jute, hemp, kenaf, sisal, abaca, pineapple leaf fiber, cotton, coir, bamboo, and wood flour have been investigated as reinforcing fibers for biocomposites. Their properties and the application to biocom­posites are described in detail in some review articles.50,52 We used wood flour (WF) made from Sanbu cedar crushed into powders through 3 mm screen mesh and mi — crofibrillated cellulose (MFC). The reason for the use of WF is as follows: Among the natural fibers, the use of waste wood generated from forest-thinning and wreck­ing of wooden building, etc. is very important for solving the severe environmental problem.53,54 Also, a massive outbreak of damaged cedar trees infected by Cerco — spora sequoiae Ellis et Everhart (“Sugi-Mizogusare” disease) which cannot be used as log and lumber is becoming a serious problem in Chiba, Japan. Fig. 4.4 shows the FE-SEM micrographs of the WF supplied from Kowa Technos, Co. Ltd. (Sammu, Chiba, Japan). The photograph at a low magnification shows that the WF particles are mainly composed of fibrous substance of ca. 0.2-1.0 mm in length. The average length and aspect ratio of the WF fibers were ca. 0.7 mm and 4.2, respectively. The photograph at a high magnification revealed that each particle is composed of fiber bunch with a rough surface.

In recent years, MFC with the diameters in the range of 10-100 nm, which is obtained through a simple mechanical process which includes refining and high pressure homogenizing, has received significant research attention as a reinforcing fibers of polymers.52,55,63 Yano et al. reported that the poly(lactic acid)/MFC bio­composites prepared by the method using acetone as a mixing solvent exhibit high strength and modulus.59 Drzal et al. reported that the mechanical properties of the composites of MFC and the bisphenol F-type epoxy resin cured with a polyether amine are improved by the silane coupling treatment of the MFC.60 It is important for the preparation of superior polymer/MFC composites to devise the dispersion method of MFC in the hydrophobic polymers and the surface treatment method of MFC. The merit of the use of bio-based epoxy resin system instead of petroleum — based epoxy resin system is that MFC can be easily dispersed in aqueous solution of GPE/TA or SPE/TA without a special surface modification of MFC. We used the MFC, trade name Celish KY-100G was supplied by Daicel Chemical Industries, Ltd. (Tokyo, Japan). This product is a 10 wt.% solid content in water suspension.